[opendtv] Re: Food for thought

On 2/21/07, Manfredi, Albert E <albert.e.manfredi@xxxxxxxxxx> wrote:

John Shutt wrote:

> How you can jump to the conclusion that MPEG-2 and MPEG-4 are
> essentially equal in bitrate requirements when use in HD is
> beyond me, beyond logic, and not supported by any data.

"Essentially equal," in the practical tests, is the key. Not identical,
not in degraded modes, not squeezing them to the limit, perhaps, but
essentially equal as implemented.

You have all the information you need:

1. Freeview uses 16-QAM, 2/3 FEC, 8 MHz channels, or roughly 15 to 16
Mb/s per multiplex. (I'm not sure of the GI, assume 1/16.)

2. Freeview assigns 4 to 5 program streams per multiplex, or on average
anywhere between 3 and 4 Mb/s per SD stream.

http://www.dgtvi.it/stat/Europa/Gran_Bretagna/Page1.html

3. HDTV in H.264 takes up the same capacity as 3 to four SDTV programs,
which means 9 to 16 Mb/s at the lower and upper limits of that estimate.

4. They tested to a max of 19.5 Mb/s, for HDTV.

You know a lot. Okay, maybe not 12 to 20 Mb/s as I had estimated, which
gave each SD stream 4 to 5 Mb/s avg, but still within the range of what
HDTV using H.262 can do, from 24p to 60p, for good HDTV.

Bert


I don't think they assign program channels it is a marketplace. AFAIK
they have spare channels on each mulitplex and the number of unused
program channels depends on if they are using 16 QAM or 64QAM.

Mux, Number of channels, owner, Number of spare channels, QAM
1,        4,                          bbc,             2,
              16
2,        9,                          3&4,             0,
              64
A,        8,                         sdn,              1,
              64
B,        5,                         bbc,              1,
              16
C,        5,                         ngw,              1,
              16
D,        6,                         ngw,              0,
              16

Right now they can do 6 program channels using 16 QAM and 9 program
channels using 64 QAM.

With MPEG-4 they are going with 8K 64 QAM I am sure so if they are
talking about the number of CURRENT channels they would lose using
MPEG-2 by going to MPEG-4 and HD then IMO we are talking about losing
3 or 4 of 9 channels per HD MPEG-4 program channel.

Your logic seems to say, if I understand it, that is by switching to
MPEG-4 and doing HD only they will sacrifice 3 or 4 SD MPEG-2 program
channels per HD program channel. Following that logic though you could
do 2 HD program channels with MPEG-4 and have either 3 SD or 1 SD
program with MPEG-2 also.

But if you went completely to MPEG-4, then you could have the 2 HD
program channels and 6 or 2 SD program channels also for a loss of
only 3 or 7 SD channels and a loss of only 1 or 5 program channels in
total.(depending on whether you sacrifice 3 or 4 channels per HD
channel)

But never the less a loss of program channels which is what the
discussion and worry was all about. Of course with the end of analog
broadcasting there will be more spectrum and more program channels I
believe in total even if every physical channel had 2 HD program
channels in it.

With MPEG-4 I believe they will be able to do 18 program SD channels,
at their current data rates, with 8K 64 QAM DVB-T.

Anyway nothing in what you quoted suggest what you tried to make of it IMO.

Bob Miller


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